Valvera Ketch had waited her whole shell-life for a map, and now the sea was stealing it back. The old chart hung nailed to her door at the top of the tide pool loft. Its first marker sat in a shallow pool below, and the water there was draining fast. She was a scallop. She could not walk. She could only clap her two shells and hop, and the pool that led to the marker grew thinner by the minute. If it dried, the map's route began nowhere. She hopped to the loft's edge and looked down. The rope bridge sagged over the emptying channel. Rocks broke the surface that had been hidden a moment ago. Below, a hermit crab dragged half of himself across the wet stone, hunting the deepest puddle. He wore no shell. His soft back curled bare in the open air. "You," Valvera called. "Can you cross that pool before it dries?" The crab stopped. He counted the rocks with one claw. "Four stones. Then two feet of open water. I have no shell. Soft parts dry fast." He pulled his claw back. "I am not scared. I just know the number." "I'm Valvera. That map is real. The whole sea says to follow it, and the first mark is drowning right now." She clapped her shells. "Help me reach it and I'll find you a shell. I build races for hermit crabs. I have a whole wall of shells." The crab's eyestalks lifted. "A wall. How many?" "Enough. But only if we move now." He climbed down the bridge. Valvera saw the flippers first, strapped near the shell wall by the slides. They were made for crabs, shaped for skating fast across water. She had built them for the races. "Take those," she said. "Buckle them on." The crab strapped the green flippers to his back legs. "Calidan Xe," he said, not looking up. "That is my name. In case the pool takes me." "It won't. Carry me on your back and skate. I can't cross alone." Calidan hesitated. Then he set his soft body low and let her slide onto his shoulders. She weighed almost nothing. He pushed off the last rock. The flippers slapped the shrinking water. Mud sucked at them halfway across. He kicked harder. The pool was two inches deep, then one. His claw touched the marker stone just as the last water slid away into the sand. Valvera pressed against the flat rock. A shape was carved there, an arrow pointing off the isle toward open sea, and beside it, a single word she could read: NEXT. "We made it," she said. "The route starts here." Calidan stared at the arrow. It pointed away from every safe pool, out past the reef, into deep water. "That way is far," he said quietly. "I still have no shell." Valvera looked at the arrow, then at the drying flats around them. The tide was gone. Nothing could cross back now.

Neville held the map to the green lantern light. His arm traced a line that bent downward, past the last marker Valvera knew. "The route drops here," he said. "Below the sunlit water. The depth signs go deeper than the light reaches." Valvera studied the marks. The path she needed ran straight down into dark, cold water. She had no way to see there. Worse, she had no way to breathe. A scallop pumped water through her shell, but not at that depth, not for that long. "I can't follow it down," she said. "Not like this." Calidan climbed to the raft's edge. He wore the shell she had traded him and her old crab flippers, still strapped to his legs. He peered over the side. "Then we're stuck," he said. "The current won't carry us down. Only across." Neville said nothing. He tucked a book under one arm and slid off the raft. He came back dragging a tangle of glossy seaweed. A green mask sat half-buried in the fronds, its carved face staring up. "Snagged on a rock below," he said. "Old diver's gear, I think." Valvera pushed at the fronds with her shell. The mask was hard and hollow. A ridge ran along its edge, shaped to seal against skin. Two dark cups fit over eyes. She turned it and found a hole at the mouth, fitted with a stiff green tube that ran back into the seaweed. "This isn't just a face," she said. Her voice sharpened. "It's a breathing mask." Neville leaned close. "The tube pulls air," he said. He traced the seaweed with one arm. "These fronds hold it, like a jar holds water. A diver could carry a breath down and read the map by the light." "Then I go down," Valvera said. "But I can't wear it. It's shaped for a face, not a shell." They both looked at Calidan. Calidan backed a step. His legs clicked on the wet peel. "Me?" "You have the flippers," Valvera said. "You have the shell. You can hold the mask, hold the lantern, and follow the marks I point to. I'll ride your back and read the map." Calidan stared at the dark water. He had spent years alone in a glass jar. He knew tight, quiet spaces. He did not know deep ones. But he fit the flippers to his feet, took the mask, and pressed it to his face. The seal held. He breathed through the tube once, twice. Valvera settled the lantern's rope in his claw. Its green core glowed steady. She climbed onto his shell and gripped tight. "Straight down," she said. "I'll count the depth marks." Calidan slipped off the raft. The water closed over them. The lantern lit a small green room in the dark. Valvera held the map close and read the first deep mark. They sank past the sunlight. The next marker waited somewhere below, and now they could reach it.